linux-kernel - Re: [PATCH] pci: avoid dead lock between device reset and sriov disable

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Date:   Tue, 10 May 2022 10:03:46 +0800
From:   Yicong Yang <yangyicong@...wei.com>
To:     Jay Zhou <jianjay.zhou@...wei.com>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bhelgaas@...gle.com>,
        <alex.williamson@...hat.com>
CC:     <yangyicong@...ilicon.com>, <weidong.huang@...wei.com>
Subject: Re: [PATCH] pci: avoid dead lock between device reset and sriov
 disable

On 2022/4/4 14:25, Jay Zhou wrote:
> Call trace of PF SRIOV disable:
> sriov_numvfs_store
>   device_lock <----------------- (1) get the device lock
>     ->sriov_configure # e.g. vfio_pci_sriov_configure
>       sriov_disable
>         pci_cfg_access_lock <--- (4) wait dev->block_cfg_access to be 0
> 
> Call trace of PF reset:
> reset_store
>   pci_reset_function
>     pci_dev_lock
>       pci_cfg_access_lock <----- (2) set dev->block_cfg_access = 1
>       device_lock <------------- (3) want to get the device lock
> 
> These two oprations would wait for each other forever if the
> code execution sequence is (1)(2)(3)(4).
> 
> Let's get the device lock and then the config access lock in
> pci_dev_lock().
> 
> Signed-off-by: Jay Zhou <jianjay.zhou@...wei.com>

The patch looks good to me,

Reviewed-by: Yicong Yang <yangyicong@...ilicon.com>

I met the same problem and tried to fix it in the same way. It's worth to be merged if somebody meets
the same problem again.
https://lore.kernel.org/linux-pci/1583489997-17156-1-git-send-email-yangyicong@hisilicon.com/

> ---
>  drivers/pci/pci.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 9ecce435fb3f..61a6db1d21f6 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5103,19 +5103,19 @@ static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
>  
>  void pci_dev_lock(struct pci_dev *dev)
>  {
> -	pci_cfg_access_lock(dev);
>  	/* block PM suspend, driver probe, etc. */
>  	device_lock(&dev->dev);
> +	pci_cfg_access_lock(dev);
>  }
>  EXPORT_SYMBOL_GPL(pci_dev_lock);
>  
>  /* Return 1 on successful lock, 0 on contention */
>  int pci_dev_trylock(struct pci_dev *dev)
>  {
> -	if (pci_cfg_access_trylock(dev)) {
> -		if (device_trylock(&dev->dev))
> +	if (device_trylock(&dev->dev)) {
> +		if (pci_cfg_access_trylock(dev))
>  			return 1;
> -		pci_cfg_access_unlock(dev);
> +		device_unlock(&dev->dev);
>  	}
>  
>  	return 0;
> @@ -5124,8 +5124,8 @@ EXPORT_SYMBOL_GPL(pci_dev_trylock);
>  
>  void pci_dev_unlock(struct pci_dev *dev)
>  {
> -	device_unlock(&dev->dev);
>  	pci_cfg_access_unlock(dev);
> +	device_unlock(&dev->dev);
>  }
>  EXPORT_SYMBOL_GPL(pci_dev_unlock);
>  
>